In connection with most activities near water there is a risk of drowning accidents. The outlook for rapidly being able to help a person, who has fallen into the water, decreases if the person by his own efforts cannot stay above the water surface. Devices for keeping a person floating at the water surface until a rescue mission can begin are known since long. One example is U.S. Pat. No. 2,165,300, which discloses an inflatable tube member in the shape of a belt. The belt is intended to be attached to the user during the entire activity performed near the water. The device is activated by means of a lever, which is located within the tube member. The lever is pressed and thereby a penetration element is displaced in order to puncture a membrane of a gas cartridge. The operation of the known belt requires quite delicate manipulation, which is hard when trying to activate the belt under water on a person who is struggling or who is unconscious. Thereto the belt as such is very hard to attach to a person who is already distressed and therefor the known belt is problematic and inexpedient to use as rescue equipment.